1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus, and more particularly to a backup belt assembly for use in a fusing system of such an apparatus.
2. Description of Related Art
In an electrophotographic image forming apparatus, such as a printer or copier, a latent image is formed on a light sensitive drum and developed with toner. The toner image is then transferred onto media, such as a sheet of paper, and is subsequently passed through a fuser assembly where heat and pressure are applied to melt and adhere the unfused toner to the surface of the media. There are a variety of devices to apply heat and pressure to the media such as radiant fusing, convection fusing, and contact fusing. Contact fusing is the typical approach of choice for a variety of reasons including cost, speed and reliability. Contact fusing systems themselves can be implemented in a variety of manners. For example, a roll fusing system consists of a fuser roll and a backup roll in contact with one another so as to form a nip therebetween, which is under a specified pressure. A heat source is associated with the fuser roll, backup roll, or both rolls in order to raise the temperature of the rolls to a temperature capable of adhering unfixed toner to a medium. As the medium passes through the nip, the toner is adhered to the medium via the pressure between the rolls and the heat resident in the fusing region (nip). As speed requirements demanded from fusing systems are increased, the size of the fuser and backup rolls must be increased, and the capability of the heat source must be expanded to sustain a sufficient level of energy necessary to adhere the toner to the medium in compensation for the shorter amount of time that the medium is in the nip. This in turn can lead to higher cost, and large rolls.
As an alternative to the roll fusing system, a belt fusing system can be used. The traditional belt fusing system consists of a single fuser roll and a backup belt that is pressed into contact with the fuser roll. A heat source may be provided within the fuser roll to generate sufficient heat within the system to adhere unfixed toner to a medium as the medium is passed between the fuser roll and the belt.
U.S. Pat. No. 5,359,401 discloses a thermal fixing roller and an endless backup belt. The belt is wrapped about four steel rollers. Because of the location of the four steel rollers, it is believed that the overall size of the fuser system is large, which is disadvantageous. U.S. Pat. No. 5,621,512 discloses a spring-biased pad for forcing a belt against a hot roll. It is believed that this design is disadvantageous due to the friction resulting from the pad making contact with the belt.
Accordingly, alternative designs of fuser systems including backup belts are desired.